The problem of spatial homogeneity in an LCoS projector
Abstract Video projectors allow interesting applications in vision sciences since they provide a large projection area. We have colorimetrically characterized a LCoS projector using a mathematical model requiring additivity and constancy of the primaries -a sigmoid function in our case. Significant differences in chromaticity in the CIELAB space, but not in lightness, were found between the center and the corners of the screen. The lack of spatial homogeneity led us to estimate the parameters of the model as a function of spatial position, using different strategies. The best result was obtained by interpolating the values of the parameters of the model determined from experimental measurem…
Analyzing the metrics of the perceptual space in a new multistage physiological colour vision model
In this work, the metric of a new multistage colour vision model, ATTD05, is assessed and a new colour difference formula is suggested. Firstly, the uniformity of the ATTD05 colour space was compared with that of CIECAM02 for some Munsell samples, because if the model yields a uniform perceptual space, we will be able to implement a colour difference formula as a Euclidian distance between two points. Secondly, we developed a new space based on the perceptual descriptors of the model: brightness, hue, colourfulness, and saturation. After that, we calculated the free parameters of the space that better fit the measured and experimental data of two datasets (small-magnitude and large-magnitud…
Application of the S-CIELAB color model to processed and calibrated images with a colorimetric dithering method.
This work uses the S-CIELAB color model to compare images that have been calibrated and processed using a colorimetric dithering method which simulates increments in viewing distance. Firstly, we obtain XYZ calibrated images by applying the appropriate color transformations to the original images. These transformations depend on whether the image is viewed on a display device or encoded by a capture device, for example. Secondly, we use a colorimetric dithering method consisting of a partitive additive mixing of XYZ tristimulus values. The number of dithered pixels depends on simulated viewing distance. The dithered tristimulus values are transformed to digital data to observe the dithering…
New iPAD-based test for the detection of color vision deficiencies.
Purpose: To develop and validate a new iPad-based color vision test (Optopad). Methods: A total of 341 student eyes were enrolled in a first comparative study between Optopad and the Isihara tests. In a second comparative study, Optopad vs. the Farnworth-Munsell test (FM 100H), a total of 66 adult eyes were included. Besides the agreement between tests, the correlation between FM 100H and Optopad outcomes were investigated. Multiple regression analysis was used to predict the total error score (TES) from contrast thresholds measured with the Optopad test. Results: The Ishihara and Optopad tests detected the same anomalous patients. Concerning FM 100H vs. Optopad, 10 subjects were diagnosed …
Reliability in perimetric multichannel contrast sensitivity measurements
Background: In this study, the reliability of perimetric contrast sensitivity measurements favouring the achromatic, the red-green and the blue-yellow post-receptorial mechanisms was analysed. Methods: A new technique, multichannel ATD perimetry, provides spatial and temporal stimuli favouring the detection by an achromatic mechanism (A), from a magno or parvocellular origin or by a red-green (RG) chromatic mechanism, with a parvocellular origin or a blue-yellow (BY) mechanism, with a koniocellular origin. The repeatability and reproducibility of contrast sensitivity measurements with these stimuli were studied in a group of 40 healthy subjects. The analysis was carried out on 21 testing po…
Software for simulating dichromatic perception of video streams
We have designed a configurable stand-alone Matlab-based software to simulate dichromatic perception of video streams. The algorithm used is an extension for video streams of the “corresponding pair algorithm” by Capilla and coworkers for simulation of dichromatic perception of images. The software allows the user to upload a video sequence and to process it using different dichromatic color vision models and viewing conditions. The output video may be generated in different spatial and temporal resolutions and file formats. The functions for Matlab environment and a stand-alone application may be downloaded from the Repository of the University of Alicante. © 2013 Wiley Periodicals, Inc. C…
Can Applications Designed to Evaluate Visual Function Be Used in Different iPads?
SIGNIFICANCE: Apple devices could be suitable for vision tests, provided that the test has been correctly adapted to the device, after considering the spatial and colorimetric characterization of the screen. PURPOSE: The majority of vision applications has not been developed by vision or colorimetry experts and suffers from conceptual and design errors that may lead average users to an erroneous assessment of their visual capabilities. The reliability of vision tests depends on the accurate generation of the necessary visual stimuli in a particular device. Our aim was to ascertain whether a given color test, designed for a colorimetrically characterized device, might be used in another simi…
Colorimetric Characterization of Mobile Devices for Vision Applications
Purpose: Available applications for vision testing in mobile devices usually do not include detailed setup instructions, sacrificing rigor to obtain portability and ease of use. In particular, colorimetric characterization processes are generally obviated. We show that different mobile devices differ also in colorimetric profile and that those differences limit the range of applications for which they are most adequate. Methods: The color reproduction characteristics of four mobile devices, two smartphones (Samsung Galaxy S4, iPhone 4s) and two tablets (Samsung Galaxy Tab 3, iPad 4), have been evaluated using two procedures: 3D LUT (Look Up Table) and a linear model assuming primary constan…
Chromatic-achromatic perimetry in four clinic cases: Glaucoma and diabetes
Color perimetry has interesting clinical application for the diagnosis and detection of certain eye conditions, due to the variations that certain diseases can cause in chromatic thresholds, both in the red-green (RG) and the blue-yellow (BY) pathways.[1,2,3,4] The separate study of the visual function of both the chromatic and achromatic mechanisms could be more efficient in detecting sensitivity variations, and such variations would not be obscured by the intrusion of other mechanisms. Currently, the supply of conventional perimeters that are capable of performing a chromatic perimetry test is very limited and with reduced options regarding the possibility of choosing the physical charact…